The present invention is directed to methods for increasing the ability of the eye to accommodate. More particularly, the invention relates to methods for increasing the amounts of accommodation in mammalian eyes including artificial intraocular lenses (IOLs), more preferably IOLs which are adapted to provide accommodating movement in the eye.
The human eye includes an anterior chamber between the cornea and iris, a posterior chamber, defined by a capsular bag, containing a crystalline lens, a ciliary muscle, a vitreous chamber behind the lens containing the vitreous humor, and a retina at the rear of this chamber. The human eye has a natural accommodation ability. The contraction and relaxation of the ciliary muscle provides the eye with near and distant vision, respectively. This ciliary muscle action shapes the natural crystalline lens to the appropriate optical configuration for focusing light rays entering the eye on the retina.
The ciliary muscle controls the shape of the natural lens through suspensory ligaments called zonules. Like most smooth muscles, the ciliary muscle has a dual innervation, receiving both sympathetic and parasympathetic fibers.
The contraction of the ciliary muscle is under parasympathetic or cholinergic control. While this parasympathetic control is predominant, sympathetic, or adrenergic, innervation opposes the cholinergic control and plays a lesser role in enabling relaxation of the ciliary muscle.
After the natural crystalline lens is removed, for example, because of cataract or other condition, a conventional, monofocal IOL can be placed in the posterior chamber. Such IOLs include an optic or lens body adapted to focus light toward the retina of the eye. One or more fixation members or haptics are coupled to the optic and function to fix the IOL in the eye. Such a conventional IOL has very limited, if any, accommodating ability. However, the wearer of such an IOL continues to require the ability to view both near and far (distant) objects. Corrective spectacles may be employed as a useful solution.
Attempts have been made to provide IOLs with accommodating movement along the optical axis of the eye as an alternative to shape changing. Examples of such attempts are set forth in Levy U.S. Pat. No. 4,409,691 and several patents to Cumming, including U.S. Pat. Nos. 5,674,282 and 5,496,366. The disclosure of each of these patents is incorporated herein by reference. Such so called accommodating IOLs include an optic or lens body adapted to focus light toward the retina and a movement assembly, having various configurations, coupled to the optic and adapted to cooperate with the eye, for example, with the ciliary muscle of the eye, to move the optic axially to obtain some degree of accommodation. The lenses of the patents noted above in this paragraph are biased to be located in the posterior-most position in the eye under rest or resting conditions. When near focus is desired, the ciliary muscle contracts and the lens moves forwardly (positive accommodation). In the absence of ciliary muscle contraction, the lens moves rearwardly to its posterior-most resting position. One problem that exists with such IOLs is that they often cannot move sufficiently to obtain the desired accommodation.
It would be advantageous to provide methods for increasing the amounts of accommodation in mammalian eyes including IOLs.